Not so long ago, whooping cough killed 5,000 to 10,000 people in the United States each year. Now that number has dropped to about 30 – but it will stay that low only if parents remain vigilant about getting their children vaccinated.

California public health officials have declared a whooping cough epidemic because statewide, nearly 1,500 cases were reported in the first half of this year, about five times the normal rate. Seven infants already have died.

The epidemic is on track to be the worst in the state in 50 years.

One reason is that increasing numbers of parents are opting out of getting their children vaccinated.

In Marin County, the parents of 7percent of incoming kindergartners in 2010 declined to have their children vaccinated. Marin also has the highest infection rate of any county in the state.

A 4-week-old baby who died on Thursday was the seventh fatality in the state this year and the first to die of whooping cough in San Diego County in nine years.

Los Angeles County has had about 290 possible pertussis cases reported, 184 of them confirmed, and three infant deaths this year, the latest of them 12 days ago.

San Bernardino County has had 17 confirmed cases and one death in 2010.

Everyone should be vaccinated, especially children, according to Dr. Kenneth Nakamoto, vice president of medical affairs for Pomona Valley Hospital Medical Center, which made vaccinations available at its health fair on Saturday.

Even adults who have been vaccinated can catch whooping cough if they haven’t been immunized for at least five or 10 years, said Maxwell Ohikhuare, health officer with the San Bernardino County Department of Public Health. Immunization wears off over time.

The state has recommended vaccinations for women who may become pregnant, grandparents – especially those who provide child care – and anyone age 7 or older who is not up to date on immunizations.

Getting immunized not only protects people getting the shots, but it also can save the lives of infants too young to be vaccinated. How sad when a relative catches the disease and brings it home to a vulnerable baby girl or boy.

The L.A. County Public Health Department cites a study that found, in cases where the source of an infant’s whooping cough infection could be identified, 41percent contracted the disease from a sibling, 38percent from the mother and 17percent from the father.

Clearly, it’s important for family members of infants to keep their own immunizations up to date.